This invention relates to the centrifuge field, and particularly to the sample retaining means used in the bores, or cavities, of a centrifuge rotor.
The advantages of the present invention are primarily intended for use in centrifuge rotors having substantially vertical bores, i.e., bores which are parallel to the spin axis. However, the modular spacer which is the subject matter of the present application is also intended to be used in centrifuge rotors having bores which are inclined with respect to the vertical rotational axis.
Furthermore, the present invention appears to have its primary advantages in conjunction with the use of "Quick Seal" sample-containing tubes, which are tubes having their cover areas formed integrally with their bodies, and sealed by fusion of a nipple, or neck, after it has been used for insertion of the fluid sample. Such tubes have proved to be highly advantageous, as compared with earlier open-top tubes, which has to be sealed with separate caps and which, therefore, had serious sealing problems.
The invention of "Quick Seal" tubes is disclosed in Nielsen application Ser. No. 912,698 titled "An Integral One Piece Centrifuge Tube", filed on June 5, 1978 and assigned to the assignee of the present application. Application Ser. No. 912,698 has been abandoned subsequent to the filing on Feb. 15, 1980 of Continuation Application Ser. No. 121,755.
Since "Quick Seal" tubes are thin-walled vessels in which the cover portion is integral with the body portion, the forces developed by centrifuge operation have a tendency to collapse the upper portion of the tube. Such tube-collapsing forces are due both to the hydrauic pressures inside the tube which act vertically on the tube during centrifugation, and to the "buckling" effect on the inner, or centripetal, portion of the tube if significant amounts of air are enclosed in the tube, either entrained in the liquid material or left in the tube because the liquid does not fill it.
In order to prevent deformation of "Quick Seal" tubes, certain precautions must be taken, particularly in providing support for the upper surface of the tube. This may be accomplished by using a supporting cap which engages, and generally conforms to, the top of the tube, even though such a cap is not required for closing, or sealing, the tube. The use of such a supporting cap is disclosed both in Nielsen application Ser. No. 912,698, and in Chulay and Nielsen application Ser. No. 122,324, titled "Supporting Cap for Sealed Centrifuge Tube", filed on Feb. 19, 1980, and also assigned to the assignee of the present application. The latter application is concerned primarily with "floating" caps for use in obliquely oriented rotor bores. In such non-vertical bores, the centrifugal force can be relied on to hold the floating cap in supporting engagement with the top of the tube.
The present application, as indicated above, is primarily concerned with problems relating to tubes in vertical rotor bores. In a vertical bore containing a tube which substantially fills the bore, the large upward forces inside the tube, generated by the hydraulic pressure, are normally opposed by a threaded plug that screws into a counterbore in the top of the rotor body. Such a threaded plug may have direct engagement with the top of the tube, or there may be a small cap inserted between the plug and the tube primarily for the purpose of partially insulating the tube from turning forces created while the plug is being screwed into, or out of, the rotor.
If a smaller amount of fluid is to be centrifuged, it is highly desirable to use a smaller tube, in order to minimize the amount of air remaining in the sealed tube. Use of a shorter tube in a vertical bore requires a spacer to fill the space between the top of the tube and the threaded plug at the top of the bore, since the tube must receive direct support against the vertically acting hydraulic pressures.
In order to make several different sample sizes usable in the same vertical rotor bore, it is desirable to have tubes of different lengths and, therefore, it is necessary to have spacers of different lengths, so that the space between the tube top and the threaded plug may be filled regardless of the size of the tube.